The present invention relates to a capsular bag ring and to an assembly constituted by such a ring and an injector therefore.
More precisely, the invention relates to an elastically deformable ring for putting into place in the capsular bag after removal of the natural lens in order to maintain the natural circular shape of the capsular bag, and particularly but not exclusively in order to make it easy subsequently to put an intraocular implant into place in the capsular bag.
It is known that the so-called xe2x80x9ccataractxe2x80x9d operation consists in removing the lens while conserving the covering of the lens which is referred to as the capsule or capsular bag. However since the bag is made of a very fine membrane which is connected to the inside wall of the eye via a ring of fibers known as zonules, the membrane tends not to conserve its regular uniform circular shape.
It is also known that after the lens has been removed, an intraocular implant is put into place in the capsular bag, which implant consists essentially in an optical portion of substantially circular shape and an elastically deformable haptic portion which serves to center the optical portion of the intraocular implant in such a manner that its optical axis coincides substantially with the optical axis of the eye. To ensure that the haptic portions perform their functions adequately, i.e. that they hold the optical portion of the implant in a central position, it is necessary for the periphery of the capsular bag, against which the free ends of the haptic portions press, to retain its circular shape and in particular it is important to avoid folds forming in the capsular bag, so as to avoid complications such as zonules being torn or the capsular bag shrinking.
To keep the capsular bag in a circular shape, proposals have already been made to install a resilient ring, usually made of polymethylmethacrylate (PMMA) whose elastic expansion serves to keep the capsular bag circular in shape. As a subsidiary point, the pressure exerted by the ring on the membrane constituting the capsular bag serves to avoid or at least limit the proliferation of parasitic cells that can obscure the capsular bag and thus degrade the patient""s vision. Such capsular bag rings are described in particular in European patent application No. 0 884 031. The ring described therein is symmetrical in shape. That shape does not make it possible to prevent folds forming in the capsular bag while the ring is being put into place. In addition, that shape does not make it possible to obtain substantially identical pressure over the entire periphery of the capsular bag.
An object of the present invention is to provide a capsular bag ring of a shape that facilitates insertion into the capsular bag without causing folds to form therein, and that enables the pressure exerted by the ring on the periphery of the capsular bag to be distributed better and thus more effectively so as to further improve maintenance of the natural circular shape of said capsular bag.
To achieve this object, the invention provides a capsular bag ring constituted by a curved elongate element presenting a first end and a second end provided with handling means, said elongate element presenting a plane of symmetry, thickness that is substantially constant in a direction orthogonal to said plane of symmetry, and inner and outer edges, said outer edge of the elongate element when at rest and in its plane of symmetry being disposed substantially tangentially at a point A to a circle of center O and of radius R that is not less than the radius of the capsular bag, said outer edge being located at the outside of said circle, said ring being characterized in that said elongate element further comprises a first branch extending between said first end and a point B, and a second branch extending between said point B and said second end, said elongate element being of a length that is substantially not less than the length of the perimeter of said circle of center O, the outer edge of said first branch being defined by a portion of a circle of center Oxe2x80x2 and of radius Rxe2x80x2, where R less than Rxe2x80x2 less than 1.10R, and in that the outer edge of the second branch of said elongate element is defined by a portion of a hyperbolic spiral of center O and joining tangentially with said portion of a circle at said point B, close to said tangential point A, whereby:
the length of any segment joining the center O to a point Mxe2x80x2 of the outer edge of the second branch is greater than the length of the segment joining the center O of the circle to a point Mxe2x80x2 of the outer edge of the first branch, the point M being such that the angle between the segment OM and the median diameter joining the center O to the tangential point A is equal to the angle between the segment OMxe2x80x2 and said median diameter; and
the radius of curvature at any point Mxe2x80x2 of the outer edge of the second branch is greater than the radius Rxe2x80x2.
It will be understood that the ring comprises a first branch substantially in the shape of a circular arc whose radius is slightly greater than that of the capsular bag and a second branch in the form of a portion of a hyperbolic spiral. The first branch is the branch that is inserted first into the capsular bag. Because this branch corresponds more or less to a semicircle of radius close to that of the capsular bag, it is easy to put this first branch into place in the capsular bag. It is only when the second branch of spiral shape is introduced into the capsular bag that the ring is subjected to significant elastic deformation of its second branch. In addition, because of its hyperbolic spiral shape, the extra diameter of the ring in said second branch compared with the diameter of the capsular bag increases only progressively. This makes it easier to put the second branch of the ring into place and thus to put the entire ring into place, since the second branch is compressed progressively.
In addition, since the elastic deformation of the ring which serves to keep the capsular bag in shape is distributed along the second branch of the ring which corresponds substantially to a semicircle, distribution of the stresses applied to the capsular bag is encouraged, thereby avoiding the risk of folds forming in said bag.
Another problem which arises is that of how to insert the ring inside the eye and the capsular bag. To do this, it is known to use an injector which is terminated by a cannula of small diameter so as to enable it to be inserted into the eye through an incision of small size, typically about 2.5 millimeters (mm) to 4 mm. The ring of the capsular bag has an orifice at at least one of its ends suitable for receiving a hook fixed to the end of a wire which enables the entire ring to be inserted inside the cannula and subsequently ejected from the cannula once the end of the cannula is inserted in the eye. Putting the end of the ring into place on the hook of the injector requires a certain amount of handling which is quite difficult because of the small dimensions of the ring and of the hook at the end of the injector wire.
There therefore exists a real problem relating to putting the capsular bag ring into place inside the injector in order to enable it to be inserted into the eye.
Another object of the invention is to provide a system comprising a capsular bag ring associated with an injector to avoid the above-mentioned prior handling.
The capsular bag ring system is characterized in that it comprises:
a capsular bag ring comprising two asymmetrical branches presenting different radii of curvature; and
a ring injector for putting said ring into place in the capsular bag, said injector comprising:
a cannula provided with an axial passage;
a body provided with a ring-handling mechanism, said mechanism comprising a flexible wire engaged in said axial passage, said wire having a first end provided with a handling member suitable for co-operating with the handling means of the ring to secure said wire temporarily to said ring, and a second end secured to means for moving said wire in said passage; and
in that when said handling member is secured to said handling means, said ring is engaged in the axial passage of said cannula via its second end over a suitable length of its second branch without applying any stress to the branch.
It will be understood that because, in accordance with the invention, the branch of the ring that is inserted in part into the cannula presents a radius of curvature that is much greater than that which is to be found in prior art rings, it is possible to insert one end of said branch into the cannula of the injector and to store the assembly until it is used by a surgeon.
Because of this large radius of curvature, the end of the second branch of the ring can remain stored in the cannula without that imparting significant deformation to the branch of the ring. It should be emphasized that such a disposition is not possible with standard type rings since the ends thereof present significant curvature which would give rise to stresses in the corresponding end of the ring likely to reduce its strength significantly after being stored for a certain length of time.